For versions up to and including 12.1.2, all the SBCs behind the SLB should be from the same cluster and share the same configuration. Load balancing across heterogenous SBC deployments are not supported (this does not apply to version 12.1.3 and newer.)
When an SBC is behind the SLB, you must enable SLB usage before making configuration changes.
If you move an SBC SWe from an SLB deployment to a non-SLB deployment (or vice versa), you must clear the configuration using the clearDBs.sh script, and then reconfigure the SBC SWe instance.